Generalizing Polygon Start/End Points

Add an option for handling "Polygon start/end points" to the Generalizer transformer. The Generalizer doesn't generalize polygon start/end points. In cases such as "Remove first colinear point from polygon", @jdh found that when you want to remove a colinear point which is also happens to be the first/last vertex in a polygon, the Generalizer doesn't remove it. In this instance, an important corner vertex is removed.